Polyolefin-ethylene/ester copolymer blend compositions

ABSTRACT

A NEW POLYETHYLENE BLEND HAVING IMPROVED STRESS CRACKING PROPERTIES, SAID BLEND COMPRISING A HIGH MOLECULAR WEIGH POLYETHYLENE AND A COPOLYMER OF ETHYLENE AND AN ESTER COMONOMER, SUCH AS ETHYL ACRYLATED, ISOBUTYL ACRYLATE AND VINYL ACETATE, THE COPOLYMER HAVING A MOLECULAR WEIGHT BELOW 15,000 AND THE ESTER COMONOMER MOIETY IN THE RANGE FROM ABOUT 20 TO ABOUT 65 WEIGHT PERCENT. A METHOD FOR PREPARING SAID BLEND WHEREIN THE COPOLYMER IS INTRODUCED INTO THE POLYETHYLENE IN THE MOLTEN STATE AS IT PASSES FROM THE POLYMERIZATION ZONE.

3,663,663 Patented May 16, 1972 3,663,663 POLYOLEFIN-ETHYLENE/ ESTERCOPOLYMER BLEND COMPOSITIONS Richard Bernie McAda, Lake Jackson, Tex.,assignorto The Dow Chemical Company, Midland, Mich.

No Drawing. Filed Sept. 13, 1968, Ser. No. 759,763

Int. Cl. C08f 29/12 U.S. Cl. 260-897 B 9v Claims ABSTRACT OF THEDISCLOSURE A new polyethylene blend having improved stress crackingproperties, said blend comprising a high molecular weight polyethyleneand a copolymer of ethylene and an ester comonomer, such as ethylacrylate, isobutyl acryla'te and "vinyl acetate, the copolymer having amolecular weight below 15,000 and the ester comonomer moiety in therange from about to about 65 weight percent. A method for preparing saidblend wherein the copolymer is introduced into the polyethylene in themolten state as it passes from the polymerization zone.

BACKGROUND OF THE INVENTION This invention relates to high molecularweight polyethylene blends having improved stress crack resistance andextrudability, and more particularly, to polyethylene blends containingsmall amounts of certain low molecular weight copolymers of ethylene andethylenically unsaturated carboxylic esters.

While high molecular weight polyethylene is known to have substantiallyimproved characteristics such as tensile strength, abrasion resistance,temperature resistance and stress crack resistance over lower molecularweight polyethylenes, it unfortunately has a very high viscosity at hightemperatures, thus making it very diificult to extrude. One of the mostsignificant disadvantages resulting from the high molecular weightpolyethylenes poor extrudability is the increased internal strainpresent in fabricated articles of the polymer. These increased internalstrains in themselves are often sufiicient to cause the polymericmaterial to crack and rupture without being subjected to environmentalstress. Generally, however, cracking and rupturing most often occurswhen the fabricated polymer is subjected to external stress.

In order to overcome this problem, various kinds and amounts ofpolymeric materials having better extrusion characteristics have beenadded to the high molecular Weight polyethylenes. For example, U.S. dat.3,183,283 teaches the addition of low molecular weight highly branchedpolyethylene to high molecular weight sparsely branched polyethylene;U.S. Pats. 2,953,541 and 3,201,- i

498 show the addition of high molecular weight copolymers of ethyleneand ethyl acrylate; and U.S. Pat. 3,182,- 101 shows the addition of highmolecular weight copolymers of ethylene and vinyl acetate. While stresscrack resistance and extrudability of high molecular weightpolyresistance and good extrudability in addition to the tensilestrength, high temperature resistance, and abrasion resistance of highmolecular weight polyethylene in order to withstand the normal stresseswhich occur when an electrical cable jacketed with the polymericmaterial is pulled through a conduit. In addition to this problem,detergents which tend to promote stress cracking must often be used tofacilitate pulling the cable through the conduit. In light of these andanalogous problems which are present in other industries, it would behighly desirable to have a polymeric material possessing the strengthand durability of high molecular weight polyethylene and theextrudability of a low molecular weight polymer or copolymer.

SUMMARY OF THE INVENTION It is therefore the object of this invention toprovide a polymeric material having these desirable characteristics.Another object is to provide a polymeric material which, whenfabricated, exhibits improved stress crack resistance. Other objects andadvantages of this invention will become apparent in the followingsummary and detailed description.

The objects of this invention have been attained in polymeric blendscomprising (1) high molecular weight polyethylene having melt index inthe range from about 0.01 to about 10.0 decigrams/minute as determinedby ASTM D-123 8-65T (Condition E) and (2) a low molecular weightcopolymer hereinafter described in detail. The copolymer component is acopolymer of ethylene and an ethylenically unsaturated carboxylic estermonomer selected from the group of vinyl esters of saturated canboxylicacids and alkyl esters of u, 3-ethylenically unsaturated carboxylicacids. The copolymer has a peak molecular weight as determined by gelpermeation chromatography in the range from about 1000 to about 15,000and the ester comonomer moiety is present in amounts from about 20 toabout '65 Weight percent based on the copolymer. The polymeric blend ofthis invention is preferably prepared by admixing the low molecularweight copolymer with molten, high molecular weight polyethylene.

The practice of this invention provides a material, hereinafter calledthe polyethylene blend, which is readily extruded to form extrudedarticles having improved stress crack resistance. The new polyethyleneblends adhere well to substantially all metal, glass, wood and plasticsurfaces. The polyethylene blends are especially useful for coatingarticles which must be exposed to extreme weather conditions, to, stresscrack promoting agents, and/or to abrasive forces. Examples of utilityinclude coating for wire cables, for glass containers, and the like.Such blends are also employed in the fabrication of shaped articles suchas bottles and the like.

DESCRIPTION OF THE PREFERRED EMBODIMENTS in the presence of a freeradical catalyst and high density,

high molecular weight polyethylenes prepared under relatively lowpressures and in the presence of a catalyst such as the ZieglerorPhillips-type.

The low molecular weight copolymer used as a minor component in theblend is a copolymer of ethylene and an ethylenically unsaturatedcarboxylic ester monomer selected from the group of vinyl esters ofsaturated carboxylic acids and alkyl esters of a,,8-ethylenicallyunsaturated carboxylic acids. Examples of suitable ester monomersinclude methyl acrylate, ethyl acrylate, butyl acrylate, isobutylacrylate, methyl methacrylate, ethyl maleate, methyl fumarate, vinylacetate, vinyl propionate and the like. Preferably the copolymercontains one of the following ester monomers: isobutyl acrylate, ethylacrylate, and vinyl acetate. An especially preferred copolymer isethylene/isobutyl acrylate copolymer as it imparts better tensilestrength, electrical properties and elongation to the polymeric blendthan do copolymers of ethylene and the other ester monomers. Othersuitable copolymers are those of ethylene and ester comonomers selectedfrom the group consisting of vinyl esters of saturated carboxylic acidshaving from 2 m 8 carbon atoms in the acid moiety and alkyl esters I ofa,;8-ethylenically unsaturated carboxylic acids having from 3 to 8carbon atoms in the acid moiety and from 2 to 8 carbon atoms in thealkyl moiety. Copolymers suitable for use in the polyethylene blends ofthis invention are characterized by their greasy, highly amorphousqualities. Suitable copolymers have peak molecular weights, asdetermined by gel permeation chromatography, in the range from about1000 to about 15,000 with preferred copolymers having a peak molecularweight between 1000 and about 10,000. In preferred copolymers thehighest molecular weight fraction is below 15,000. Gel permeationchromatographic methods for determining molecular weights of polymersare described by J. C. Moore in the J. Polymer Sci. A., 2, 835 (1964).See also L. H. Tung, J. Appl. Polymer Sci., 10, 345 (1966) and W. N.Smith, J. Appl. Polymer Sci., 11, 639 (1967). Since such copolymers havemelt flow viscosities above those which can be accurately measured byASTM D- 1238-65T at 190 C. and 2.16 kilograms, it is necessary to altersome of the conditions of this test method in order to obtain moremeaningful values. Using the apparatus and procedures of ASTM D-1238-65Texcept that the diameter of the plastometer orifice is reduced to 0.020inch and the test temperature is 80 C., the copolymers utilized in thisinvention exhibit melt flow viscosities in the range from about 0.01decigram/minute to about 50 decigrams/minute. Based on crudeinterpolation from these values and the changes in conditions, thecopolymers would probably exhibit melt flow viscosities over 2000decigrams/minute under conditions of ASTM D- 1238 65T(E). The copolymersof this invention have an ester comonomer moiety in the range from about20 to about 65 weight percent of the copolymer with the preferred estermoiety being in the range from about 30 to about 50 weight percent.

The low molecular weight copolymers are readily prepared by polymerizingthe corresponding monomers at high temperatures and pressures in thepresence of a free radical catalyst. A suitable means of preparation isdescribed in US. Pat. 2,395,381 except that higher temperatures andincreased catalyst concentration are used. In a preferred method up toabout 20 weight percent based on the total comonomer weight of a telomersuch as propylene is added to the polymerization zone to inhibit theformation of high molecular weight copolymers.

The blends of this invention comprise from about 85 to about 95 weightpercent of the high molecular weight polyethylene and from about toabout weight percent of the low molecular weight copolymer with thepreferred blends containing from about 92.5 to about 95 weight percentof the polyethylene and from about 5 to about -7.5 weight percent of thecopolymer. Preferred concentrations of these two components varysomewhat with the average molecular weight of the copolymer, theconcentration of ester monomer in the copolymer, the particular estermonomer, and the melt index of the polyethylene component. For example,as the molecular weight of the copolymer is decreased, the environmentalstress crack resistance of the resulting blend is increased. As theester comonomer concentration in the copolymer is increased, theenvironmental stress crack resistance of the blend is similarlyincreased. As the melt index of the polyethylene component becomeslower, extrusion of the blend becomes more difficult, and internalstrains of articles fabricated therefrom are increased. As a generalrule the better blends are those having total ester comonomer moietiesranging from about '1 to about 10 weight percent with the best blendshaving ester comonomer moieties. ranging from about 1 to about 5 weightpercent.

Although the final blend is essentially composed of high molecularweight polyethylene and the low molecular weight copolymer, smallamounts of other ingredients such as carbon black, inorganic fillers,antioxidants and the like are optionally included. Such ingredientsshould not be present in amounts greater than about 10 weight percentbased on the blend; otherwise the stress crack resistance and tensilestrength of the blend may be reduced considerably. In one embodiment ofthis invention the blend contains up to about 9 weight percent of carbonblack and up to about 2 weight percent of antioxidant, both percentagesbeing based on the blend.

The blends of this invention are readily prepared by mixing the drycomponents in conventional mixing apparatus such as Banbuiy mixers,steam heated two roll mill mixers, screw type extruders and the like.Such blends are also suitably prepared by admixing slurries or solutionsof the components and then removing the liquid vehicles.

If the components are admixed in the dry state, it is desirable tointroduce the low molecular weight copolymer into the polyethylenecomponent while the polyethylene component is in the molten state. Inaddition, due to the processing problems often caused by the highviscosity of the polyethylene component, it is preferable to introducethe copolymer into the polyethylene as soon as possible in order tolower the viscosity of the polyethylene. In a preferred embodiment, thecopolymer is introduced to the polyethylene in the molten state as thepolyethylene passes from the polymerization zone to a fabricationapparatus such as an extruder. Although it is desirable to add thecopolymer as soon as possible in order to reduce viscosity of thepolyethylene and to assure adequate mixing of'the'components, care mustbe taken that the copolymer is not added at a point in thepolymerization zone where it will interfere with polymerization ofethylene. For example when the polyethylene component is prepared by ahigh pressure process wherein ethylene is polymerized in a high pressurereactor and the resulting polyethylene in the molten state is removedtherefrom to a separation apparatus where unreacted ethylene and otherundesirable materials are separated from the polyethylene, the lowmolecular weight copolymer is preferably injected at a point between thereactor and the separation apparatus. The copolymer may be injected at apoint within the reactor if it is near the exit of the reactor. Byintroducing the copolymer at the earliest possible stage, it is mucheasier to obtain a more uniform final blend of the polymeric components.

The final blends of this invention have melt flow viscosities low enoughto enable them to be worked easily and have substantially improvedstress crack resistance, especially in the presence of stress crackpromoting detergents.

In the subsequentexamples, the following test methods were employed forthe measurements referred-to herein.

Melt Index (M.I.) (melt flow rate,

This procedure was modified by using a-- one-centistoke silicone oil atKHg.

The Standard Environmental Stress Crack Resistance .(Std. E.S.C.R.) wasmeasured according to ASTM D-1693- 60T with the exception of beingtested in 10% Igepal 'and 100% Hostapal as well as the 100% Igepalprescribed by the ASTM method.

The Brabender Torque Values are used as an indication of the rheology ofmolten thermoplastics. These values are determined by using a BrabenderPlasti-Corder obtained from C(W. Brabender Instruments Co. of SouthHackensack, NJ. For these measurements the machine was equipped withstandard oil-heated measuring head,

#5 roller blade style mixer blades and a torque recording chart. Themixing'head was heated to 180 C. 01"140" C.i0.5 C. and operated at 63r.p.m. Fifty grams of polyiner was charged into the mixing head and thetorque recorder and stop watchwere started! The torque (in meter-grams)was noted at one-minute intervals starting at two minutes and therecordings continued to eleven minutes. Initial torque is the reading attwo minutes and final torque is the reading at eleven minutes.

Brabendered E.S.C.R. refers to a measurement of the environmental stresscrack resistance (E.S.C.R.) after the polymer has been worked on theBrabender mixer. For these determinations the mixer head is operated at154 C.i0.5 C. and 125 r.p.m. and the sample is mixed or worked for onehour. The sample is then removed from mixer head and molded in a platendie at 170 C. to prepare specimens according to ASTM D- 1693-60T. Themolding is done by holding the sample under 5 tons pressure (6" ram) forthree minutes, then under 25 tons pressure for 2 minutes. The moldedsample is then taken from the press and immediately placed in water of atemperature of -20 C. and left in the water for 10 minutes. The sampleis then conditioned in a 70 C. oven for 18 hours, then removed from theoven and conditioned for 72 hours at room temperature (-23 C.). Fromthis sample, specimens are cutand tested in detergent according to theprocedure prescribed by ASTM 'D' 1693-60T with the exception that aswell as the 100% Igepal prescribed, 10% Igepal and 100% Hostapal arealso used.

The following examples are given to illustrate'more clearly theprinciple and practice of this invention and are not for the purpose oflimitation. Throughout this specification and claims, all parts andpercentages are by weight unless otherwise indicated.

Example 1 Example 2 The process of Example 1 was repeated except that 95parts of the same polyethylene and 5 parts of an ethylcue/vinyl acetate(V.A.) copolymer were blended. The copolymer had a peak molecular weightin the range of about 6 000-8000 and a vinyl acetate content of about 35percent. The resulting blend was tested and the results are recorded inTable I along with the data for Example 1 and the data for the,unbl'ended polyethylene control for comparison purposes.

TABLE 13 Polyethylene Blend of Blend of control Example 1 Example 2 Meltindex 0.16 0.35 0.23.

Density 00177.. Yield strength (p.s.i.) Tensile strength (p.s.Elongation (percent) 62 Vicat softening pt. C.).-.. 92.... 84 86.Percent comonomer in blend- None 3.8 (i-BA).... 1.8 (V.A.). Brabendertorque at 180 0.. 2,350/1,590.-.. 2,150/1,420... 2,220 [1,480. E.S.C.R.(Barbendered):

10% epal 9/10/1 hr 1/10/168 hrs... 0/10/168 hrs.

100% Hostapal 10/10/1 hr..... 5/10/32 hrs.-.. 0/10/168 hrs. E.S.C.R.(Standard ASTM meth.):

10% Igepal 0/10/168 hrs... 0/10/168 hrs... 0/10/168 hrs. 100% Igepal0/10/168 hrs... 0/10/168 hrs... 0/10/168 hrs. 100% Hostapal 0/10/168hrs... 0/10/168 hrs... 0/10/168 hrs.

Example 3 The procedure of Example 1 was again repeated except that 7.5parts of the ethylene/isobutyl acrylate (iBA) c0- polymer described inExample 1 was blended with 92.5 parts of polyethylene having a meltindex of 2.48 decigrams/minute and a density of 0.9173. The propertiesof the blend are compared with the properties of the unblendedpolyethylene control employed in the blend of this example, in Table II.

Example 4 The procedure essentially of Example 1 was employed to blend 5parts of the ethylene/ vinyl acetate (V.A.) co polymer described inExample 2 with parts of the polyethylene described in Example 3. Theproperties of the blend are shown in Table II.-

Vicat softening pt. C.).--. 88.. 2 87. Percent reactive eomonornerNone... 3.8 (i-BA).... 1.8 (V.A.).

in blend.

Brabender torque at 140 0.. 1,830/1,440.... 1,760/1,260... 1,780/1,320.E.S.C.R. b (Standard ASTM):

10% Igepal 10/10/ 1 hr-.. 5/10/4 hrs...- 6/10/3 hrs. Igepal 10/10/ 1hr... 5/10/5 hrs.... 7/10/1 hr.

n Not an example of this invention. b See in Table 1.

Example 5 Prior to blending with a low molecular weight copolymer, asample'of polyethylene having a melt index of 0.1 decigram/minute anddensity of 0.918 was admixed with carbon black and 4,4 thio bis(G-tert-butyl-mcre'sol) by homogeneously blending 90 parts of the moltenpolyethylenewith 10 parts of a molten carbon black concentrate. Theconcentrate Was composed of 26 parts of carbon black, 0.5 part of4,4'-thio-bis-(6-tert-butyl-mcresol), and 73.5 parts of a polyethylenehaving a melt index of 0.5 g./ 10 min. and a density of 0.918. Theproperties of this control blend are shown in Table III for comparisonpurposes. 93.9 parts of the control blend described immediately abovewas homogeneously blended 35 percent.

The properties of the blend are shown in Table III.

TABLE III Polyethylene blend Blend of Blend of (control) n Example 5Example 6 Melt index 0.11 0.21 0.14. Density 0.9314 0.9200 0.0321.Percent carbon black in 2.8 2.41 2.2.

blen

Yield strength (p.s.i.) 1,430 1,238 1,310. Tensile strength (p.s.i.)2,050. .9

Percent elongation. \icat softening pt. (1.). Percent cornonomer moietyNon 86 89. 2.6 (i-BA 1.8 (VA). in blend. Brabender torque at 180 C2,050/1,550... 2,080/1,510... 2,000/1,540.

Low tgmp. brittleness at 1/3 3/ 70 C. Dissipation factor at 100 0.00040.0012 0.0015.

kHz. Dielectric Constant at 100 2,48 2.57 2.20.

kl-Iz. Brabendered E.S.C.R.:

10% Igepal 0/10/0hrs 0/10/108l11's... 0/10/168 hrs. 100% Hostapal 4/6/4hrs 0/6/108 hrs 0/6/168 hrs.

a Not an example of this invention. See in Table 1.

Example 7 In order to prepare a base blend for this and followingexample, ten parts of the carbon black concentrate described in Example5 was homogeneously blended with 90 parts of a polyethylene having beenpreviously prepared in a tubular reactor and having a density of 0.9162and a melt index of 0.18 decigram/minute. The properties of this basecontrol blend are shown in Table IV for comparison purposes.

The procedure of Example 6 was employed to homogeneously blend 92.5parts of the base control blend with 7.5 parts of the ethylene/isobutylacrylate (i-BA) copolymer described in Example 1. The properties of thisblend are shown in Table IV.

Example 8 The procedure of Example 6 was again employed to homogeneouslyblend 92.5 parts of the base control blend described in Example 7 with7.5 parts of the ethylene/ vinyl acetate (VA) copolymer described inExample 2. The properties of this blend are shown in Table IV.

TABLE IV Polyethylene base blend Blend of Blend of (control) Example 7Example 8 Meltindcx 0.25

Dissipation factor at 10 kHz 0.0001 Dielectric constant at lOkIIz. 2.582.6l 2.61. Brabender torque at 180 0.. 2,060/1,620-.. 1,850/1,300.1,820/1,420. Drabendered E.S.C.R.

10% Igepal l0/l0/1.5 hrs 1/0/108 hrs 0/10/168 hrs. 100% Hostapal 4/4/05hrs- 0/4/108 hrs 0/3/108 hrs.

11 Not an example of this invention. b See in Table 1.

8 Example 9 In a reactor train comprising in continuous sequence a highpressure stirred autoclave reactor, a high pressure separator, and a lowpressure separator, ethylene was polymerized under conditions requiredto yield a polyethylene having a melt index of less than 0.1decigram/min. and a density of about 0.918. The polyethylene, after itwas formed in the stirred autoclave section, was extruded into the highpressure separator. Then at a point between the high pressure separatorand the low pressure separator, a molten copolymer of ethylene andisobutyl acrylate having an average molecular weight of about 3000 andan isobutyl acrylate moiety of about percent was added to the moltenpolyethylene at a rate so that the copolymer comprised 7 to 8 percent ofthe total blend. Subsequently a molten polyethylene/carbon blackconcentrate composed of 26 percent of carbon black, 1 percent of 4,4-thio-bis-(6-tert-butyl-m-cresol), and 73 percent of polyethylene havinga density of 0.918 and a melt index of 0.5 decigram/minute was alsoblended with the polyethylene at a rate so that the concentratecomprised 10 per cent of the total blend. The resulting blend had thefollowing properties:

Melt index 0.18 Density 0.9328 Yield strength (p.s.i.) 1210 Tensilestrength (p.s.i.) 1960 Percent elongation 535 Percent carbon black 2.68Dissipation Factor at 100 kHz 0.0006 Dielectric Constant at 100 kHz 2.65

Brabender torque at 180 C 2210/1610 Brabender E.S.C.R. (hours) 10%Igepal0/10/l68 hrs.

100% Igepal-0/10/168 hrs.

100% Hostapal0/10/168 hrs. 1 See (b) in Table I.

Example 10 Polyethylene (control) B Blend with copolymer Melt index...

Tensile strength (p. Elongation (percent) Vicat softening pt. C.)Brabender torque at 180 C E.S.C.R. (Brabendcred):

10% Igepal 100% Hostapal....

88 80. l,020/l,0l0 1,800/1,520.

6/10/2 hrs 0/10/330 hrs. 10/10/1 hr 0/10/330 hrs.

* Not an example of this invention. See in Table I.

What is claimed is:

1. A polyethylene blend having improved stress crack resistancecomprising (1) from about to about weight percent of a high molecularweight polyethylene having melt index in the range from about 0.01 toabout 10.0 decigrams/minute as determined by ASTM D1238 65T(E) and (2)from about 5 to about 15 weight percent of a copolymer of ethylene andat least one ester comonomer selected from the group consisting of alkylesters of 04,5 ethylenically unsaturated carboxylic acids having alkylmoieties of 1 to 8 carbon atoms and vinyl esters of saturated carboxylicacids having from 2 to 8 carbon atoms, said copolymer having peakmolecular weight within the range from about 1000 to about 15,000, theester comonomer moiety being present in proportion from about 20 toabout 65 weight percent based on the copolymer.

2. The polyethylene blend according to claim 1 wherein the estercomonomer is isobutyl acrylate.

3. The polyethylene blend according to claim 1 wherein the estercomonomer is ethyl acrylate.

4. The polyethylene blend according to claim 1 wherein the estercomonomer is vinyl acetate.

5. The polyethylene blend according to claim 1 wherein the copolymer hasa peak molecular weight in the range from about 1000 to about 10,000.

6. The polyethyelne blend according to claim 1 wherein the copolymer hasfrom about 30 to about 50 weight percent of the ester comonorner.

7. The polyethylene blend according to claim 1 which also contains up toabout 9 weight percent of carbon black and up to about 2 weight percentof antioxidant, said percentages being based on the blend.

8. The polyethylene blend according to claim 1 wherein the highmolecular weight polyethylene has melt index in the range from about0.01 to about 2.0 decigrams/minute as determined by ASTM D-l23865T(E).

9. In the art of removing high molecular weight polyethylene from a highpressure polymerization reactor to a low pressure extrusion apparatuswherein the polyethylene in a molten state passes from the reactor tothe extrusion apparatus, the improvement which comprises introducingfrom about 5 to about 15 weight percent based on the total resultingblend of polyethylene and copolymer of a copolymer of ethylene and atleast one ester comonomer selected from the group consisting of alkylesters of 0:, 3 ethylenically unsaturated carboxylic acids having alkylmoieties of 1 to 8 carbon atoms and vinyl esters of saturated carboxylicacids having from 2 to 8 carbon atoms, said copolymer having peakmolecular weight from about 1000 to about 15,000, the ester comonomermoiety being present in proportion from about 20 to about weight percentbased on the copolymer, at a point between the reactor and the extrusionapparatus such that the introduction is near enough to the reactor toassure adequate mixing of the copolymer with the polyethylene but not sonear as to interfere with the polymerization of the ethylene in thepolymerization reactor.

References Cited UNITED STATES PATENTS 3,248,359 4/1966 Maloney 260413,201,498 8/1965 Brunson et al. 260897 2,953,541 9/1960 Pecha et al.26045.5 3,183,283 5/1965 Reding 260897 OTHER REFERENCES Billmeyer,Textbook of Polymer Science, pp. 366-367 (1962).

SAMUEL H. BLECH, Primary Examiner C. SECCURO, Assistant Examiner US. Cl.X.R.

ll7-l24 E, 128.4, 161 UT, 161 -UZ; 26028.5 A,

28.5 AV, 21.2 R, 41 R CER'ilFiCA'iE o co on Patent: No. 3, 3 Dated I 16y 97 Inventofls) Richar d Bernie McAda Itis certified that error appearsin the above-identified patent and that said Letters Patent are herebycorrected as shown below:

In Table III Column T, between lines 15 and 35 please make the followingcorrections:

the third line under the last column, change "2.2" to 2.7.

the fifth line under the column headed "Blend of Example 5" change"1.921" to --l,92l-.

line 12 under column headed "Polyethylene blend" change "2A8" to--2.h8--

line 12 under column headed "Blend of Example 6", change "2.29" to 2.59

Column 9, line 15, change "polyethyelne" to polyethylene- Signed andsealed this 10th day of October 1972.

(SEAL) Attest:

EDWARD 1 1 1.FILJE'TGIIER J'R.a ROBERT GOTTSCHALK Attesting OfficerCommissioner of Patents

